1. Field of the Invention
The present invention relates to the structure of a metallic engaging element that is attached to a side edge portion of a fastener tape of a slide fastener and a slide fastener including the engaging elements.
2. Description of the Invention
In some type of slide fastener for use in opening/closing, for example, clothes and bags, engaging elements made of a synthetic resin obtained by injection molding or engaging elements continuous in a coil or zigzag shape made of a synthetic resin are formed integrally to a fastener tape by molding or sewing. On the other hand, various kinds of slide fasteners have been provided that include metallic engaging elements in order to express a feature from design viewpoint, texture and massiveness. Known materials available for the metallic engaging elements include rolled materials of nickel silver, brass, aluminum or the like and cast materials.
As slide fasteners using metal as a material of engaging elements, there are old type fasteners about 100 years old which employ 100% cotton yarns as its fastener tape and use pressed components made of nickel silver for, for example, the engaging elements and bottom end stop, and products which satisfy military standard. Some of these old type slide fasteners are called vintage type slide fastener, and attract public attention among mania as a consumer use purpose also from the reason of historical values and appearance. Thus, such slide fasteners have been dealt with vividly today also.
The military standard slide fastener not only assures the usage condition and environmental condition but also requires process control and quality control for guaranteeing the specification more precisely than the consumer use products in terms of the quality of a raw material and manufacturing process. As a result, the product price of the slide fastener is boosted largely so that it cannot meet demands for consumer use purposes in which the design aspect is regarded as the most important factor.
As this kind of the slide fastener having the conventional metallic engaging elements, for example, U.S. Pat. No. 1,615,113 (patent document 1), U.S. Pat. No. 1,659,480 (patent document 2) and German Patent No. 462647 (patent document 3) have been known. In these slide fasteners, a sheet metal is punched out to obtain small pieces, and the resulting pieces are formed by pressing and attached in line at predetermined intervals by press-fitting on the side edge portion of the fastener tape so as to arrange metallic engaging elements.
The slide fastener engaging element described in the patent document 1 is comprised of: a head portion having a coupling opening for coupling the engaging elements attached to stringers opposing with each other or an coupling pawl; a pair of right and left leg portions for attachment to one side edge of a fastener tape; and a body portion for connecting the leg portions with the head portion. The slide fastener engaging element described in the patent document 3 is comprised of: a head portion having a coupling neck portion and a coupling concave portion to be coupled with an engaging element attached to a mating side stringer; a pair of right and left leg portions for attachment to one side edge portion of a fastener tape; and a body portion for connecting the leg portion with the head portion.
The leg portions of the engaging elements described in the patent documents 1 and 3 each are formed symmetrically so as to branch to right and left sections from the body portion. The pair of right and left leg portions each is constituted of a sheet-like nipping portion having two notch portions for sandwiching the front and rear surfaces of the side edge portion of the fastener tape and a leg portion side wall erected from the sheet-like nipping portion. The section of the leg portion is substantially L shaped. Leg portion outside wall surfaces of the leg portion side wall parallel to the side edge of the fastener tape serve as a sliding surface which makes contact with the inside surface of right and left flanges of the slider in the slide fastener, thereby forming a substantially flat surface.
The slide fastener engaging element described in the patent document 2 is comprised of: a head portion for coupling the engaging elements attached to a mating stringer; a pair of right and left leg portions for sandwiching a side edge portion of a fastener tape from the front and rear surfaces thereof; and a body portion for connecting the leg portion with the head portion. The sheet-like nipping portions of the pair of right and left leg portions each have two cut-out portions for nipping two columns of core threads formed on the side edge of the fastener tape. However, no leg portion side wall is formed on the sheet-like nipping portion, and thus, the leg portion is flat, not formed into the L shape in its section.
Generally, the material of the slide fastener engaging elements described in the patent documents 2 and 3 is formed of a rolled sheet material made of alloy called nickel silver, that is produced by adding zinc and nickel to copper which is a base material. Using nickel silver as the material of the engaging element makes it easy to satisfy the standard about environment resistance, durability, lateral pulling force and upward pushing force, etc. due to the physical property of the nickel silver.
However, the nickel silver is an expensive material because it is alloy containing nickel. In addition, when the nickel silver is processed, a die or press die having a high hardness need to be used for processing because the tensile yield point of the material is high, thereby increasing the product price of the slide fastener. Thus, employing the nickel silver as the material of the engaging element causes such an inconvenience that use of the vintage type slide fastener is difficult to expand in public for consumer use purpose.
In some cases, the engaging element of the vintage type slide fastener made of nickel silver may be replaced with a material having a low yield point such as brass while its shape is kept unchanged in order to reduce the price of the slide fastener. In such cases, the pair of leg portions for sandwiching the fastener tape becomes likely to be opened, so that there is a possibility that the fixing strength of the engaging element to the fastener tape is dropped.
When the lateral pulling force or the upward pushing force is applied to the slide fastener in engagement, the weakened fixing strength of the engaging element poses the following disadvantages. That is, the engaging elements are inclined to be opened, the engaging elements tilt with respect to the fastener tape, the engaging element deviates from the fastener tape, or the engaging element slips out of the fastener tape.